This invention relates to a tire having at least one component of a rubber composition comprised of two distinctly different rubbers. The first rubber is a terpolymer rubber which contains pendant hydroxyl groups and is derived from a diene hydrocarbon, vinyl aromatic compound monomers and a hydroxyl containing a co-monomer. The second rubber contains a nitrile moiety.
Vehicular tires, particularly pneumatic tires, are sometimes provided with a component such as, for example, a tread which is comprised of a rubber composition which contains two or more rubbers or elastomers.
Elastomer blends which contain, for example, cis 1,4-polybutadiene and styrene/butadiene elastomers are often used for such tire component (e.g. tire tread). Rubber compositions may also contain various amounts of additional diene-based elastomers such as, for example, one or more of cis 1,4-polyisoprene, cis 1,4-polybutadiene, medium vinyl polybutadiene, styrene/butadiene copolymers, isoprene/butadiene copolymers, and minor amounts of 3,4-polyisoprene.
For the above mentioned styrene/butadiene copolymer rubber, both emulsion polymerization prepared and organic solvent polymerization prepared styrene/butadiene copolymer elastomers have been used. Also, historically, emulsion polymerization derived terpolymer elastomers comprised of units derived from styrene and 1,3-butadiene together with an additional monomer have been prepared and proposed for use for various products.
U.S. Pat. No. 5,902,852 discloses the modification of an asphalt cement with a rubbery terpolymer prepared by emulsion polymerization which is comprised of repeat units derived from conjugated diolefin monomer, such as, for example, cis 1,4-polybutadiene, vinyl aromatic monomer such as styrene and a small amount of hydroxypropyl methacrylate (HPMA).
U.S. Pat. No. 6,057,937 discloses use of a terpolymer of cis 1,4-polybutadiene, styrene and, for example hydroxypropyl methacrylate in rubber compositions.
Hydroxy-containing polymers are disclosed in U.S. Pat. Nos. 4,150,014, 4,150,015, 4,152,308 and 4,357,432.
The present invention relates to a rubber composition which is particularly suited for use in a tire. The composition is characterized by containing two very dissimilar rubbers. The first rubber is a terpolymer having a pendant hydroxyl group. The second rubber contains a nitrile moiety.
There is disclosed a rubber composition comprising, based on 100 parts by weight (phr) of rubber
(A) from 10 to 90 phr of a terpolymer rubber comprised of repeat units derived from
(1) 30 to 89 weight percent of a conjugated diene monomer which contains from 4 to 8 carbon atoms;
(2) 10 to 50 weight percent of a vinyl substituted aromatic monomer; and
(3) 1 to 20 weight percent of at least one co-monomer selected from the group consisting of the following general formulas I, II, and III: 
wherein R represents a hydrogen atom or an alkyl group containing from 1 to 8 carbon atoms;
wherein R1 represents a saturated alcohol group containing from 1 to 8 carbon atoms;
(B) 10 to 90 phr of a rubber comprised of repeat units derived from
(1) 30 to 99 weight percent of a conjugated diene monomer which contains from 4 to 8 carbon atoms;
(2) zero to 50 weight percent of a vinyl substituted aromatic monomer; and
(3) 1 to 20 weight percent of an olefinic unsaturated nitrile selected from the group consisting of acrylonitrile, methacrylonitrile, ethacrylonitrile, crotononitrile and mixtures thereof.
In addition, there is disclosed a tire having a component comprising, based on 100 parts by weight (phr) of rubber
(A) from 10 to 90 phr of a terpolymer rubber comprised of repeat units derived from
(1) 30 to 89 weight percent of a conjugated diene monomer which contains from 4 to 8 carbon atoms;
(2) 10 to 50 weight percent of a vinyl substituted aromatic monomer; and
(3) 1 to 20 weight percent of at least one co-monomer selected from the group consisting of the following general formulas I, II, and III: 
wherein R represents a hydrogen atom or an alkyl group containing from 1 to 8 carbon atoms;
wherein R1 represents a saturated alcohol group containing from 1 to 8 carbon atoms;
(B) from 10 to 90 phr of a rubber comprised of repeat units derived from
(1) 30 to 99 weight percent of a conjugated diene monomer which contains from 4 to 8 carbon atoms;
(2) zero to 50 weight percent of a vinyl substituted aromatic monomer; and
(3) 1 to 20 weight percent of an olefinic unsaturated nitrile selected from the group consisting of acrylonitrile, methacrylonitrile, ethacrylonitrile, crotononitrile and mixtures thereof.
In the description of this invention, the terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d when used herein, are used interchangeably, unless otherwise prescribed. The terms xe2x80x9crubber compositionxe2x80x9d, xe2x80x9ccompounded rubberxe2x80x9d and xe2x80x9crubber compoundxe2x80x9d, if used herein, are used interchangeably to refer to xe2x80x9crubber which has been blended or mixed with various ingredients and materialsxe2x80x9d and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
The term xe2x80x9cphrxe2x80x9d if used herein, and according to conventional practice, refers to xe2x80x9cparts of a respective material per 100 parts by weight of rubber, or elastomerxe2x80x9d.
The Tg of an elastomer, if referred to herein, refers to a xe2x80x9cglass transition temperaturexe2x80x9d of the elastomer which can conveniently be determined by a differential scanning calorimeter at a heating rate of 10xc2x0 C. per minute.
The first critical ingredient in the rubber composition is the terpolymer rubber derived from the conjugated diene monomer, vinyl substituted aromatic monomer and hydroxyl containing co-monomer. The terpolymer will comprise from 10 to 90 phr of the total 100 parts by weight of rubber in the composition. Preferably, from 25 to 75 phr will be the terpolymer.
Representative examples of conjugated diene monomers which may be used include 1,3-butadiene, isoprene, 1,3-ethylbutadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-cyclooctadiene, 1,3-octadiene and mixtures thereof. Preferably, the conjugated diene is 1,3-butadiene. The terpolymer will contain repeat units derived from 30 to 89 weight percent of the conjugated diene. Preferably, from 50 to 80 weight percent of the terpolymer will be derived from the conjugated diene.
The terpolymer is also derived from a vinyl substituted aromatic monomer. The vinyl-substituted aromatic compound may contain from 8 to 16 carbon atoms. Representative examples of vinyl substituted aromatic monomers are styrene, alpha methyl styrene, vinyl toluene, 3-methyl styrene, 4-methyl styrene, 4-cyclohexylstyrene, 4-para-tolylstyrene, para-chlorostyrene, 4-tert-butyl styrene, 1-vinylnaphthalene, 2-vinylnaphthalene and mixtures thereof. Preferably, styrene is used. The terpolymer will contain repeat units derived from 10 to 50 weight percent of the vinyl substituted aromatic monomer. Preferably, from 20 to 40 weight percent of the terpolymer is derived from a vinyl substituted aromatic monomer.
The terpolymer is also derived from a hydroxyl containing monomer. One to 20 weight percent of the terpolymer is derived from the hydroxy containing monomers. Preferably, from 1 to 5 weight percent of the terpolymer is derived from these monomers. The hydroxyl containing co-monomer may be a hydroxyl alkyl acrylate of formula I or a hydroxy alkyl acrylamide of formula II and/or III, as seen below. 
wherein R represents a hydrogen atom or an alkyl group containing from 1 to 8 carbon atoms. Preferably, R is a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms. R1 is a saturated alcohol group containing from 1 to 8 carbon atoms. Preferably, R1 has from 1 to 4 carbon atoms. The saturated alcohol group may be a primary, secondary or tertiary alcohol group.
The hydroxy alkyl acrylate co-monomer of structural formula I may be hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate (HPMA isomer), 3-hydroxypropyl methacrylate (HPMA isomer), 3-phenoxy-2-hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyhexyl methacrylate, hydroxyoctyl methacrylate and mixtures thereof. Preferably the hydroxyalkyl acrylate co-monomer of structural formula I is hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate and mixtures thereof.
When mixtures of such co-monomers are selected, the mixtures may comprise 2-hydroxypropyl methacrylate and 3-hydroxy-propyl methacrylate (HPMA isomers), a blend in weight ratio, for example, in a range of from about 85/15 to about 60/40, respectively.
The hydroxy alkyl acrylamide co-monomer of structural formula II and/or III may be hydroxymethyl methacrylamide, 2-hydroxyethyl methacrylamide, 2-hydroxypropyl methacrylamide and 3-hydroxypropyl methacrylamide, 3-phenoxy-2-hydroxy-2-hydroxypropyl methacrylamide, hydroxybutyl methacrylamide, hydroxyhexyl methacrylamide, hydroxyoctyl methacrylamide and mixtures thereof.
The microstructure, namely the cis and trans structures, of the terpolymer are considered herein to be somewhat typical for an emulsion polymerization derived styrene/butadiene copolymer elastomer.
Preferably, the terpolymer elastomer is further characterized by a glass transition (Tg) in a range of about 0xc2x0 C. to about xe2x88x9265xc2x0 C., with a range of from about xe2x88x9250xc2x0 C. to about xe2x88x9220xc2x0 C. being particularly preferred.
The terpolymer may have a Mooney viscosity (M/L 1+4 at 100xc2x0 C.) that varies. Suitable terpolymers have a Mooney viscosity as low as 20 to as high as 91. Preferably, the Mooney viscosity ranges from 50 to 90.
The aforesaid terpolymer elastomer can be synthesized, for example, by using conventional elastomer emulsion polymerization methods. For example, a charge composition comprised of water, one or more conjugated diolefin monomers, (e.g. 1,3-butadiene), one or more vinyl aromatic monomers (e.g. styrene) and the HPMA, a suitable polymerization initiator and emulsifier (soap). The terpolymerization may be conducted over a relatively wide temperature range such as for example, from about 4xc2x0 C. to as high as 60xc2x0 C., although a temperature in a range of about 4xc2x0 C. to about 10xc2x0 C. may be more desirable.
The emulsifiers may be added at the onset of the polymerization or may be added incrementally, or proportionally as the reaction proceeds. Anionic, cationic or nonionic emulsifiers may be employed.
The second essential ingredient in the rubber compound is a rubber containing a nitrile moiety. This rubber will comprise from 10 to 90 phr of the total 100 parts by weight of rubber in the composition. Preferably, from 25 to 75 phr will be the rubber containing a nitrile moiety. The rubber may be derived from two or more polymerizable monomers. For example, the rubber is comprised of repeat units derived from
(A) 30 to 89 weight percent of a conjugated diene monomer which contains from 4 to 8 carbon atoms;
(B) zero to 50 weight percent of a vinyl substituted aromatic monomer; and
(C) 1 to 20 weight percent of a nitrile containing co-monomer.
Preferably, from 60 to 80 weight percent of the nitrile containing rubber is derived from the conjugated diene, from 20 to 40 weight percent is a derived vinyl substituted aromatic monomer and from 1 to 5 weight percent is derived from a nitrile containing co-monomer.
Representative examples of suitable conjugated diene monomers and vinyl substituted aromatic monomers which may be used to prepare the nitrile containing polymer include those used in preparation of the terpolymer with hydroxyl groups. Preferably, 1,3-butadiene and styrene are used, if any.
Representative examples of suitable olefinically unsaturated nitriles which may be used include acrylonitrile, methacrylonitrile, ethacrylonitrile, crotononitrile and mixtures thereof. Preferably, the olefinically unsaturated nitrile is acrylonitrile.
Preferably, the nitrile containing rubbers is characterized by a glass transition (Tg) in a range of about 0xc2x0 C. to about xe2x88x9265xc2x0 C., with a range of from xe2x88x9250xc2x0 C. to xe2x88x9220xc2x0 C. being particularly preferred.
The nitrile containing rubbers may have a Mooney viscosity (M/L 1+4 at 100xc2x0 C.) that varies. Suitable examples of nitrile containing rubbers have a Mooney viscosity as low as 20 to as high as 91. Preferably, the Mooney viscosity ranges from 50 to 80.
The rubber having the nitrile moiety can be prepared by any of the known general techniques of polymerization, including free radical solution polymerization, emulsion or suspension polymerization techniques by batch, continuous or intermittent addition of the monomers and other components. The preferred method of preparation is an emulsion polymerization. The polymerization is preferably carried out in an aqueous medium in the presence of emulsifiers and a free-radical generating polymerization initiator at a temperature of from about 0xc2x0 C. to 100xc2x0 C., in a substantial absence of molecular oxygen. Preferably, the olefinically unsaturated nitrile is continuously or incrementally added to the reactor depending if the process is continuous or batch.
In the emulsion polymerization, other ingredients such as acids, electrolytes, chain transfer agents, chelating agents, and similar ingredients known in the art to be useful in emulsion polymerization may be employed in any of the feed streams.
A representative chelating agent useful in preparing the composition of the present invention is the tetrasodium salt of ethylenediaminetetracetic acid. Conventional amounts of the chelating agents may be used.
The electrolytes traditionally used in the latex industry may be used to prepare the composition of the present invention. Typical of these electrolytes are tetra sodium and potassium pyrophosphates, tri sodium and potassium phosphates, dipotassium and disodium hydrogen phosphates, potassium and ammonium carbonates, bicarbonates and sulfites. More specifically, tetra sodium and potassium pyrophosphates and tri sodium and potassium phosphates are preferred. The concentrations of the electrolytes are those minimum amounts necessary for achieving the desired effect.
Conventional modifiers or chain transfer agents may be used to prepare the elastomers of the present invention. Examples of these chain transfer agents include mercaptans, bromoform, carbon tetrabromide, and carbon tetrachloride. The most preferred are mercaptans. Examples of suitable mercaptans are n-octyl mercaptan, n-nonyl mercaptan, tertiary-nonyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, sec-dodecyl mercaptan, tertiary-dodecyl mercaptan, tertiary-tetradecyl mercaptan, tertiary-hexadecyl mercaptan, secondary-hexadecyl mercaptan, n-hexadecyl mercaptan, or mixtures of mercaptans. It is possible to employ any of such modifiers, individually or in combination contingent to achieving desired polymer properties. With the monomers which are used to prepare the composition of the present invention, it is preferable that a modifier be present. Tertiary-dodecyl mercaptan is a preferred chain transfer agent. Chain transfer agents are conventionally used at a level of 0.05 to 0.8 phm (parts per one hundred parts of monomers). The chain transfer agent may be either premixed with the primary monomers or charged separately.
Suitable free radical polymerization initiators used to prepare the compositions of the present invention are those which are traditionally utilized in emulsion polymerization. Typical initiators or catalysts are persulfates, water soluble peroxides, and hydroperoxides. Typical examples of these initiators are ammonium, potassium and sodium persulfate, hydrogen peroxide, tertiary-butyl hydroperoxide, cumene hydroperoxide, para-menthane hydroperoxide, pinane hydroperoxide, and peroxy carbonates. Preferably, the hydroperoxides are used.
Other catalysts such as redox catalysts may be employed. One such redox system consists of ferrous sulfate heptahydrate, and sodium formaldehyde sulfoxylate. The advantages of the redox catalyst are well known in the art and usually allow lower polymerization temperatures. The initiators or catalysts are used in amounts sufficient to cause polymerization.
A listing of various emulsifiers and detergents which may be used to prepare the composition of the present invention is given in the book McCutcheon""s Emulsifiers and Detergents, 1981 Annuals,xe2x80x9d which is incorporated herein by reference in its entirety. The emulsifiers useful in this invention may be a combination of one or more emulsifiers of the anionic, cationic, non-ionic, or amphoteric class of surfactants. Suitable anionic emulsifying agents are alkyl sulfonate, alkyl aryl sulfonates, condensed naphthalene sulfonates, alkyl sulfates, ethoxylated sulfates, phosphate esters, and esters of sulfosuccinic acid. Representative of these emulsifiers are sodium-alpha-olefin (C14-C16) sulfonates, alkali metal or ammonium dodecylbenzene sulfonates, disodium dodecyl diphenyloxide disulfonate, disodium palmityl diphenyloxide disulfonate, sodium, potassium or ammonium linear alkyl benzene sulfonate, sodium lauryl sulfate, ammonium alkyl phenolethoxylate sulfate, ammonium or sodium lauryl ether sulfate, ammonium alkyl ether sulfate, sodium alkyl ether sulfate, sodium dihexyl sulfosuccinate, sodium dicyclohexylsulfosuccinate, sodium diamyl sulfosuccinate, sodium diisobutylsulfosuccinate, disodium ethoxylated nonyl phenol half ester of sulfosuccinic acid, tetrasodium N-(1,2-dicarboxyethyl)-N-octadecyl sulfosuccinate, disodium bistridecyl sulfosuccinate, sodium salt of alkyl aryl polyether sulfate, lauryl alcohol ether sulfate, sodium salt of condensed naphthalene sulfonic acid, complex phosphate ester of ethylene oxide adduct and mixtures thereof Also, the sodium or potassium salts of rosin acid and sodium and potassium salts of mixed fatty acids and mixtures thereof may be used. The amount of emulsifying agents (surfactants) may vary. Conventionally, the concentration of the emulsifying system is normally in the range of from about 0.3 to 8.0 phm in the polymerization system.
In addition to the two dissimilar rubbers, the rubber or rubber component may contain one or more additional conjugated diene-based elastomers. When used, the additional rubber or rubbers generally range from 0 to 80 phr of the total rubber used. Preferably, the additional rubber will range from 10 to 50 phr with 90 to 50 phr being the total of the two dissimilar rubbers. More specifically, the additional rubbers range from 10 to 50 phr, the terpolymer ranges from 10 to 80 and the rubber containing nitrile may range from 10 to 80 phr.
Representative of various additional conjugated diene-based elastomers for use in this invention include, for example, cis 1,4-polyisoprene rubber (natural or synthetic), cis 1,4-polybutadiene, high vinyl polybutadiene having a vinyl 1,2 content in a range of about 30 to about 90 percent, styrene/butadiene copolymers (SBR) including emulsion polymerization prepared SBR and organic solvent polymerization prepared SBR, styrene/isoprene/butadiene terpolymers, isoprene/butadiene copolymers and isoprene/styrene copolymers.
Representative of rubber reinforcing carbon blacks for the tire tread rubber composition are those, for example, having an Iodine value (ASTM D1510) in a range of about 80 to about 160, alternatively about 100 to about 150, g/kg together with a DBP (dibutylphthalate) value (ASTM D2414) in a range of about 70 to about 200, alternatively about 100 to about 150 cm3/100 g. Representative of such carbon blacks can easily be found in The Vanderbilt Rubber Handbook, 1978 edition, Page 417.
The term xe2x80x9cphrxe2x80x9d as used herein, and according to conventional practice, refers to xe2x80x9cparts by weight of a respective material per 100 parts by weight of rubber, or elastomer.xe2x80x9d
In addition to the terpolymer rubber having pendant hydroxyl groups and rubber containing a nitrile moiety in the rubberized component of the tire, conventional fillers may be also present. The amount of such conventional fillers may range from 10 to 250 phr. Preferably, the filler is present in an amount ranging from 20 to 100 phr.
The commonly employed siliceous pigments which may be used in the rubber compound include conventional pyrogenic and precipitated siliceous pigments (silica), although precipitated silicas are preferred. The conventional siliceous pigments preferably employed in this invention are precipitated silicas such as, for example, those obtained by the acidification of a soluble silicate, e.g., sodium silicate.
Such conventional silicas might be characterized, for example, by having a BET surface area, as measured using nitrogen gas, preferably in the range of about 40 to about 600, and more usually in a range of about 50 to about 300 square meters per gram. The BET method of measuring surface area is described in the Journal of the American Chemical Society, Volume 60, Page 304 (1930).
The conventional silica may also be typically characterized by having a dibutylphthalate (DBP) absorption value in a range of about 100 to about 400, and more usually about 150 to about 300.
The conventional silica might be expected to have an average ultimate particle size, for example, in the range of 0.01 to 0.05 micron as determined by the electron microscope, although the silica particles may be even smaller, or possibly larger, in size.
Various commercially available silicas may be used, such as, only for example herein, and without limitation, silicas commercially available from PPG Industries under the Hi-Sil trademark with designations 210, 243, etc; silicas available from Rhodia, with, for example, designations of Z1165MP and Z165GR and silicas available from Degussa AG with, for example, designations VN2 and VN3, etc.
Commonly employed carbon blacks can be used as a conventional filler. Representative examples of such carbon blacks include N110, N121, N220, N231, N234, N242, N293, N299, S315, N326, N330, M332, N339, N343, N347, N351, N358, N375, N539, N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907, N908, N990 and N991. These carbon blacks have iodine absorptions ranging from 9 to 145 g/kg and DBP No. ranging from 34 to 150 cm3/100 g.
It may be preferred to have the rubber composition for use in the tire component to additionally contain a conventional sulfur containing organosilicon compound. Examples of suitable sulfur containing organosilicon compounds are of the formula:
Zxe2x80x94Alkxe2x80x94Snxe2x80x94Alkxe2x80x94Zxe2x80x83xe2x80x83IV
in which Z is selected from the group consisting of 
where R2 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; R3 is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is an integer of 2 to 8.
Specific examples of sulfur containing organosilicon compounds which may be used in accordance with the present invention include: 3,3xe2x80x2-bis(trimethoxysilylpropyl) disulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl) disulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl) tetrasulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl) octasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl) tetrasulfide, 2,2xe2x80x2-bis(triethoxysilylethyl) tetrasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl) trisulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl) trisulfide, 3,3xe2x80x2-bis(tributoxysilylpropyl) disulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl) hexasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl) octasulfide, 3,3xe2x80x2-bis(trioctoxysilylpropyl) tetrasulfide, 3,3xe2x80x2-bis(trihexoxysilylpropyl) disulfide, 3,3xe2x80x2-bis(tri-2xe2x80x3-ethylhexoxysilylpropyl) trisulfide, 3,3xe2x80x2-bis(triisooctoxysilylpropyl) tetrasulfide, 3,3xe2x80x2-bis(tri-t-butoxysilylpropyl) disulfide, 2,2xe2x80x2-bis(methoxydiethoxysilylethyl) tetrasulfide, 2,2xe2x80x2-bis(tripropoxysilylethyl) pentasulfide, 3,3xe2x80x2-bis(tricyclonexoxysilylpropyl) tetrasulfide, 3,3xe2x80x2-bis(tricyclopentoxysilylpropyl) trisulfide, 2,2xe2x80x2-bis(tri-2xe2x80x3-methylcyclohexoxysilylethyl) tetrasulfide, bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl 3xe2x80x2-diethoxybutoxy-silylpropyltetrasulfide, 2,2xe2x80x2-bis(dimethyl methoxysilylethyl) disulfide, 2,2xe2x80x2-bis(dimethyl sec.butoxysilylethyl) trisulfide, 3,3xe2x80x2-bis(methyl butylethoxysilylpropyl) tetrasulfide, 3,3xe2x80x2-bis(di t-butylmethoxysilylpropyl) tetrasulfide, 2,2xe2x80x2-bis(phenyl methyl methoxysilylethyl) trisulfide, 3,3xe2x80x2-bis(diphenyl isopropoxysilylpropyl) tetrasulfide, 3,3xe2x80x2-bis(diphenyl cyclohexoxysilylpropyl) disulfide, 3,3xe2x80x2-bis(dimethyl ethylmercaptosilylpropyl) tetrasulfide, 2,2xe2x80x2-bis(methyl dimethoxysilylethyl) trisulfide, 2,2xe2x80x2-bis(methyl ethoxypropoxysilylethyl) tetrasulfide, 3,3xe2x80x2-bis(diethyl methoxysilylpropyl) tetrasulfide, 3,3xe2x80x2-bis(ethyl di-sec. butoxysilylpropyl) disulfide, 3,3xe2x80x2-bis(propyl diethoxysilylpropyl) disulfide, 3,3xe2x80x2-bis(butyl dimethoxysilylpropyl) trisulfide, 3,3xe2x80x2-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenyl ethoxybutoxysilyl 3xe2x80x2-trimethoxysilylpropyl tetrasulfide, 4,4xe2x80x2-bis(trimethoxysi lylbutyl) tetrasulfide, 6,6xe2x80x2-bis(triethoxysilylhexyl) tetrasulfide, 12,12xe2x80x2-bis(triisopropoxysilyl dodecyl) disulfide, 18,18xe2x80x2-bis(trimethoxysilyloctadecyl) tetrasulfide, 18,18xe2x80x2-bis(tripropoxysilyloctadecenyl) tetrasulfide, 4,4xe2x80x2-bis(trimethoxysilyl-buten-2-yl) tetrasulfide, 4,4xe2x80x2-bis(trimethoxysilylcyclohexylene) tetrasulfide, 5,5xe2x80x2-bis(dimethoxymethylsilylpentyl) trisulfide, 3,3xe2x80x2-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide, 3,3xe2x80x2-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide.
The preferred sulfur containing organosilicon compounds are the 3,3xe2x80x2-bis(trimethoxy or triethoxy silylpropyl) sulfides. The most preferred compounds are 3,3xe2x80x2-bis(triethoxysilylpropyl) disulfide and 3,3xe2x80x2-bis(triethoxysilylpropyl) tetrasulfide. Therefore as to formula I, preferably Z is 
where R3 is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms being particularly preferred; alk is a divalent hydrocarbon of 2 to 4 carbon atoms with 3 carbon atoms being particularly preferred; and n is an integer of from 2 to 5 with 2 and 4 being particularly preferred.
The amount of the sulfur containing organosilicon compound of formula IV in a rubber composition will vary depending on the level of other additives that are used. Generally speaking, the amount of the compound of formula IV will range from 0.5 to 20 phr. Preferably, the amount will range from 1 to 10 phr.
It is readily understood by those having skill in the art that the rubber composition would be compounded by methods generally known in the rubber compounding art, such as mixing the various sulfur-vulcanizable constituent rubbers with various commonly used additive materials such as, for example, sulfur donors, curing aids, such as activators and retarders and processing additives, such as oils, resins including tackifying resins and plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants and antiozonants and peptizing agents. As known to those skilled in the art, depending on the intended use of the sulfur vulcanizable and sulfur vulcanized material (rubbers), the additives mentioned above are selected and commonly used in conventional amounts. Representative examples of sulfur donors include elemental sulfur (free sulfur), an amine disulfide, polymeric polysulfide and sulfur olefin adducts. Preferably, the sulfur vulcanizing agent is elemental sulfur. The sulfur vulcanizing agent may be used in an amount ranging from 0.5 to 8 phr, with a range of from 1.5 to 6 phr being preferred. Typical amounts of tackifier resins, if used, comprise about 0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts of processing aids comprise about 1 to about 50 phr. Such processing aids can include, for example, aromatic, naphthenic, and/or paraffinic processing oils. Typical amounts of antioxidants comprise about 1 to about 5 phr. Representative antioxidants may be, for example, diphenyl-p-phenylenediamine and others, such as, for example, those disclosed in the Vanderbilt Rubber Handbook (1978), Pages 344 through 346. Typical amounts of antiozonants comprise about 1 to 5 phr. Typical amounts of fatty acids, if used, which can include stearic acid comprise about 0.5 to about 3 phr. Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typical amounts of waxes comprise about 1 to about 5 phr. Often microcrystalline waxes are used. Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.
Accelerators are used to control the time and/or temperature required for vulcanization and to improve the properties of the vulcanizate. In one embodiment, a single accelerator system may be used, i.e., primary accelerator. The primary accelerator(s) may be used in total amounts ranging from about 0.5 to about 4, preferably about 0.8 to about 1.5, phr. In another embodiment, combinations of a primary and a secondary accelerator might be used with the secondary accelerator being used in smaller amounts, such as from about 0.05 to about 3 phr, in order to activate and to improve the properties of the vulcanizate. Combinations of these accelerators might be expected to produce a synergistic effect on the final properties and are somewhat better than those produced by use of either accelerator alone. In addition, delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization retarders might also be used. Suitable types of accelerators that may be used in the present invention are amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates. Preferably, the primary accelerator is a sulfenamide. If a second accelerator is used, the secondary accelerator is preferably a guanidine, dithiocarbamate or thiuram compound.
The mixing of the rubber composition can be accomplished by methods known to those having skill in the rubber mixing art. For example the ingredients are typically mixed in at least two stages, namely at least one non-productive stage followed by a productive mix stage. The final curatives including sulfur vulcanizing agents are typically mixed in the final stage which is conventionally called the xe2x80x9cproductivexe2x80x9d mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) than the preceding non-productive mix stage(s). The rubber and terpolymer rubber having pendant hydroxyl groups and/or rubber containing a nitrile moiety are mixed in one or more non-productive mix stages. The terms xe2x80x9cnon-productivexe2x80x9d and xe2x80x9cproductivexe2x80x9d mix stages are well known to those having skill in the rubber mixing art. The two dissimilar rubbers may be added as a separate ingredient or in the form of a masterbatch. The rubber composition containing these two dissimilar rubbers, as well as the sulfur-containing organosilicon compound, if used, may be subjected to a thermomechanical mixing step. The thermomechanical mixing step generally comprises a mechanical working in a mixer or extruder for a period of time suitable in order to produce a rubber temperature between 140xc2x0 C. and 190xc2x0 C. The appropriate duration of the thermomechanical working varies as a function of the operating conditions and the volume and nature of the components. For example, the thermomechanical working may be from 1 to 20 minutes.
The rubber composition containing the rubber and these two dissimilar rubbers may be incorporated in a variety of rubber components of the tire. For example, the rubber component may be a tread (including tread cap and tread base), sidewall, apex, chafer, sidewall insert, wirecoat or innerliner. Preferably, the compound is a tread.
The pneumatic tire of the present invention may be a race tire, passenger tire, aircraft tire, agricultural, earthmover, off-the-road, truck tire and the like. Preferably, the tire is a passenger or truck tire. The tire may also be a radial or bias, with a radial being preferred.
Vulcanization of the pneumatic tire of the present invention is generally carried out at conventional temperatures ranging from about 100xc2x0 C. to 200xc2x0 C. Preferably, the vulcanization is conducted at temperatures ranging from about 110xc2x0 C. to 180xc2x0 C. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air. Such tires can be built, shaped, molded and cured by various methods which are known and will be readily apparent to those having skill in such art.